Exercise stair device

ABSTRACT

Apparatus which simulates the exercise obtained while climbing stairs includes two hydraulically phased steps retained in adjacent inclined tracks in which the steps are supported in a hydraulically open-ended system, with the phasing of the steps being controlled by a pair of in-line hydraulic actuators, one each associated with a step, in which fluid forced from one actuator with a downward movement of the associated step is channeled through a variable restricted orifice to the other actuator to raise the other step. In one lightweight, compact embodiment, the device is collapsed down to a compact size through the use of steps which are foldable to the track, and through the use of a track foldable to the frame. In its open position the lower portion of the frame props up the track at an appropriate climbing angle, with upper portions of the frame extending above the track to serve as handles positioned above the center of travel of the steps.

FIELD OF INVENTION

This invention relates to exercise devices and more particularly to anexercise stair which simulates the exercise encountered during theclimbing of stationary stairs.

BACKGROUND OF THE INVENTION

One exercise device which simulates the exercise encountered during theclimbing of stationary stairs is described in U.S. Pat. No. 3,970,302,issued to Richard McFee. In this exercise device, moveable steps areprovided on an inclined track, with the counterforce being providedhydraulically, in one case by actuation of a hydraulically dampedvariable pivot lever and in another case by a hydraulic motor. In bothof these cases, the steps are moved in opposition or phased mechanicallysuch that when one step is moved downwardly by the weight of anindividual, the other step is moved upwardly. In the McFee patent, themechanical phasing of the steps is accomplished by a wire or chain fromone stair to the other over a pulley or hydraulic motor sprocket. Themechanical phasing assures that when one step goes up by a predeterminedamount, the other step will come down by this predetermined amount. Itshould be noted however that should the wire or chain break, the stepsare unsupported and an individual can fall off the device. As will beappreciated, mechanical phasing results in a large number of movingparts and mechanical linkages which are noisy, cumbersome and expensive.Moreover, both the pivoted arm embodiment and the hydraulic pumpembodiment of the McFee patent are difficult to implement because theydo not accommodate the expansion of the hydraulic fluids occasioned bytemperature increases associated with use, as energy expended by theuser's efforts is absorbed. Also significant backlash accompanies use ofthese two embodiments which is annoying. Moreover, in the pumpembodiment it is extremely difficult to provide a pump which actssymmetrically in both directions. Additionally, neither of the two McFeeembodiments allow for compact packaging because the phasing apparatus isbulky and in one embodiment is accomplished by a large number ofmechanical parts not conveniently housed in a flat package which wouldpermit compact storage and ready portability.

Additionally, in any conveniently sized pivoted arm embodiment, toadjust the counterforce by 5% for a 100 lb. person corresponding to achange in climbing rate from 60 ft. per minute to 63 ft. per minute, thefulcrum of the pivoted arm is to be changed by less than 1/8 inch, whichis virtually impossible to do. This severely limits repeatability of thecounterforce setting and the ease with which the counterforce can bevaried. Repeatability of the counterforce setting is important becauseexercise regimens specified by exercise physiologists often progress inintensity from one week to another by increments of only 5% or less.

It will, however, be appreciated that the device described in theabove-mentioned patent has advantages over other types of exercisedevices such as rowing machines, stationary exercise bicycles, andendless belt walkers.

By way of further background, with respect to exercise bicycles, thesedevices rely on a pedal driven wheel and either a roller or brakes forproviding the counterforce. The problem with these types of exercisedevices is the extra amount of effort necessary to start the wheelmoving from a dead stop. Moreover in the case of brakes, after thestatic coefficient of friction has been overcome, the brake pads orstrap provide relatively little counterforce. Thus, adjustment of such adevice is difficult.

Aside from getting the wheel started, in all of the above-mentioneddevices, the amount of counterforce is not readily adjustable and isnon-linear. More specifically, the above-mentioned exercise cycles areto a certain extent speed sensitive in that the counterforce applied tothe reaction part actuated by the user is speed dependent. For instancein the exercycle, the counterforce lessens substantially as the userexercises since the heating up of the friction pads results in adecreased coefficient of friction during exercise. This is also true forthe resilient rim exercycles in which the roller forms a standing wavewhich makes the exercycle easier to pedal.

By way of further background, perhaps one of the more important problemsin terms of home use exercise devices is the noise and vibrationassociated with these devices. When these devices are utilized inapartments, for instance, the noise and vibration can be so significantthat the user is required to forego the use of the exercise device dueto the annoyance it causes neighbors. Moreover, if the user prefers towatch television or listen to radio during exercise, the exercise deviceis sometimes so noisy that it drowns out either the television or theradio. In all of the prior art devices mentioned above, there are aplurality of mechanical parts and mechanical linkages which areinherently noisy. For instance, bike chains, rollers and pivoted leversare amongst those mechanical devices which create considerable noiseduring operation.

SUMMARY OF THE INVENTION

The subject device is an all-hydraulic, quiet exercise stair devicehaving a pair of steps which move in opposition along an inclined track.The steps are linked together hydraulically in an open-ended system inwhich the fluid from one hydraulic actuator supporting one step ismetered through a variable orifice metering valve to the actuator forthe other step and visa-versa so that the rate at which the steps may beactuated is infinitely and linearly variable by controlling the flowrate from one actuator to the other. The subject device has theadvantages of repeatability and easy adjustability of flow rate whichsets the speed, gentle failure mode, permits fluid expansion, low noiseand compactness.

It is a feature of this hydraulic system that restricting the orificedecreases the flow rate which increases the time for a step to descendwith a given body weight. This means that the exercise rate is slowerand therefore the equivalent climbing rate is slower. To obtain moreexercise, the orifice is opened to permit more rapid stair climbing.This means that the number of step actuations per minute may beincreased, and in fact can be increased to such an extent that it isequivalent to running up stairs or a slope. Thus, aerobic exercise isincreased with an increase in the orifice of the metering valve, therebyincreasing heart rate, respiration rate, and resultant caloric burn-off.The system thus controls the maximum rate at which a user may exercisein a very convenient fashion.

Moreover, the increased volume of hydraulic fluid that occurs as aresult of the increased temperature during exercise is accommodated by arise in the position of the steps. Thus, the present inventionaccommodates thermal expansion of the hydraulic fluid during exercisewithout special valving, accumulators or additional cooling elementssince expansion of the fluid merely increases the step height.

As important, the steps are phased hydraulically rather thanmechanically. The use of the totally hydraulic system without mechanicalphasing results in an exceptionally quiet, simple system. Moreover inits failure mode, the subject device deposits the individual gently tofloor level as opposed to abruptly dropping him.

The hydraulic actuator utilized to support the stairs or steps mayemploy either a hydraulic ram or a piston cylinder. The hydraulic ramhas only one seal, namely the rod seal, as opposed to a rod seal and apiston seal used in a piston cylinder. The use of hydraulic rams avoidsinternal leakage problems associated with piston seals because no pistonseal is used. Moreover, the hydraulic ram is lower in manufacturingcost. With respect to external leakage in open-ended systems, hydraulicrams are preferable because low cost piston cylinders invariably leakoil which can damage carpeting or rugs.

In one embodiment, the hydraulic cylinders are flexibly mounted to abase plate and are provided with a flexible interconnection between theend of a hydraulic cylinder and the metering valve, such that theactuator rods in the hydraulic cylinders may move off-axis without sideforces on the rod seal. The main purpose of the flexible mounting is toeliminate side forces on the rod seal. Elimination of side loadinggreatly enhances rod seal life and avoids leaks. Since leaks are a majorfault mode of hydraulic systems, this is an important product lifefactor. The reliability of this type mounting system also increases thesafety of the device as well as the longevity of the hydraulicactuators.

The compactness and stowability of the subject exercise stair in oneembodiment is due in part provided by in-line, hydraulic cylinderscarried totally within the track so as to achieve a flat package.Additionally, for storage the steps are foldable to the track and thetrack is folded to a frame to which it is hinged. The lower portion ofthe frame serves to prop up the track at a predetermined angle, withupper portions of the frame extending above the track serving ashandles. In a preferred embodiment the handles are telescoping and arepositioned above the center of travel of the steps. Various frame/trackfolding methods are described hereinafter.

When not in use, the frame is pivoted or swung to a point parallel toand flush with the track. In one embodiment, the steps are folded downto the plane of the track such that the entire device may beconveniently stowed, especially under a bed. With the frame swung intoplace parallel to the track, wheels on the frame contact the floor suchthat the entire device may be moved wheelbarrow fashion.

While the subject exercise stair is extremely quiet in operation due tothe simplicity of its operation, the exercise stair can be made evenquieter through the utilization of oil-impregnated wooden skids for thesteps instead of the rollers used in the aforementioned McFee patent. Inone embodiment the oil-impregnated wooden skid is 60% oil by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the subject invention will be betterunderstood in connection with the detailed description taken inconjunction with the drawings of which:

FIG. 1 is a diagrammatic illustration of the subject exercise stairillustrating hydraulic phasing and the hinged frame configuration;

FIG. 2 is a schematic illustration of a prior art system for phasingstairs illustrating a mechanical phasing technique;

FIG. 3 is a schematic illustration of the hydraulic system utilized formechanical phasing of the stairs of FIG. 1;

FIG. 4 is a schematic illustration of the hydraulic phasing system ofFIG. 3, illustrating the direction of the counterforce provided for theactuator coupled to the stair which is moving downwardly;

FIG. 5 is a diagrammatic illustration of the stair track illustratingthe hydraulic actuator support for the stair steps and flexible basepivots for the actuators;

FIG. 6 is a diagrammatic illustration of the flexible joint for the baseof the actuator of FIG. 5;

FIG. 7 is a side view of the exercise stair showing the folding of theframe to the track and also illustrating the collapse of the steps to aposition flush with the track;

FIG. 8 is a diagrammatic illustration of the storage of the subjectexercise stair underneath the bed in its folded or collapsed condition;

FIG. 9 is a side view of the subject exercise stair illustrating inphantom, the swinging of the frame away from the track;

FIG. 10 is a diagrammatic illustration of a portion of the track and aportion of the frame in their assembled position;

FIG. 11 is a diagrammatic illustration of an alternative track foldingmethod;

FIG. 12 is a diagrammatic illustration of a still further track foldingmethod;

FIG. 13 is a diagrammatic illustration of the positioning of a carryingstrap on one side of the track to facilitate carrying; and,

FIG. 14 is a diagrammatic illustration of an alternative hydaulicphasing system using rods in tension and piston seals as opposed to rodsin compression and rod seals.

DETAILED DESCRIPTION

In order to provide for an exercise device in which the counterforce tothe individual is easily controlled and referring now to FIG. 1, in oneembodiment an exercise stair 10 is provided with a dual track 12 and aframe 14 which is double-hinged at 16 and 18 with a hinge strap 20 suchthat the assembled exercise device takes on an A-frame configurationwith an inclined track 12 and an inclined frame 14.

Extensible arms 22 and 24 are telescoped from the upper porttions 26 and28 of upstanding frame members 30 and 32 such that the handle portions33 are positioned above the tracks preferably at the midpoint in thetravel of the steps in their tracks. A bottom cross member 34 isprovided to complete the bottom of the frame, whereas a horizontalspacing member 36 is provided at a point adjacent hinge point 18, yetfar enough from the track to prevent pinching if spacing member 36 isheld during opening of the device. The bottom of the frame is providedwith wheels 38 as illustrated.

Inclined track 12 is provided with tracks generally indicated at 40 and42. Channels 44 and 46 in respective tracks house carriages 50 and 52.Steps 54 and 56 are mounted to carriages 50 and 52 respectively, withthe carriages being supported hydraulically by in-line, full strokehydraulic actuators 58 and 60.

Actuators 58 and 60 are connected hydraulically at their bases by anadjustment or metering valve 62 which controls the counterforce to theindividual, here illustrated in dotted outline at 64, as the individualshifts his weight to a step which is to be moved downwardly. As will bedescribed, in one embodiment carriages 50 and 52 are mounted forreciprocation within their respective tracks in a sliding fit.

In operation, the individual utilizing the exercise stair steps down onone step which offers resistance to the individual's weight inaccordance with the setting of valve 62. When the step associated withthis downward pressure reaches its lower limit, the individual thenshifts his weight to the upper step and the process is repeated suchthat the equivalent of stair climbing exercise is achieved.

As mentioned hereinbefore, the phasing of the steps, that is themovement of one step relative to the other, is achieved completelyhydraulically with no mechanical phasing of the steps involved.Referring to FIG. 2, in the prior art steps 70 and 72 are mechanicallylinked together by a cable or chain 74 which runs over a pulley 76 suchthat as one step descends, the other moves up to the exact extent thatthe opposing step moves down. It has been found that it is not necessaryto obtain the feel of stair climbing, that one step move up precisely bythe same amount that the other step moves down. This permits completehydraulic phasing of the steps such as illustrated in FIGS. 3 and 4, andalso provides an extremely quiet exercise device.

Referring to FIG. 3, in a preferred embodiment each actuator is ahydraulic ram as opposed to a piston cylinder which has both pistonseals as well as rod seals. Each ram is a rod 78 mounted for translationin a cylinder. Note that the only sealing is that which is accomplishedat the top of the actuators by rod seals 82 as illustrated. The rodseals are preferable to piston seals because rods can be inexpensivelymanufactured to tighter tolerances than can the inside dimension of aconventional hydraulic cylinder to which a piston is sealed. While it ispossible to utilize conventional hydraulic cylinders with piston sealsat the lower ends of the rods, e.g. piston cylinders, in an open-endedsystem it has been found that piston seal leakage can occur whichresults in exterior oil leakage and loss of stroke and phasing. Forclosed systems if piston seal leakage occurs, stroke and phasing can berestored by use of a bypass involving an additional circuit and valve toreturn the fluid to the proper side of the piston.

It will be appreciated that that which produces the hydraulic pressureis the end of the rod which is the only surface of the actuator on whichthe fluid works. Referring to FIG. 4, when a force is applied to the rodin actuator 60 by virtue of the weight of the individual applied to step56, a counterforce f(v) acts against end 80 of the rod within actuator58. This flow rate is dependent upon the pressure across variableorifice 84 in which the pressure P₁ to the left of this orifice isgreater than the pressure P₂ at the time that the force f is applied torod 78 in actuator 58.

With respect to actuator 58, at the time force is applied to actuator60, rod 78 in actuator 60 will be in its lower position. In terms of theoperation of the device, when the individual shifts his weight to step56, there is no weight applied to step 54 and therefore there is no backpressure across orifice 84 assuming that step 54 is completelyunweighted. With step 54 unweighted, the rod within actuator 60 moves inthe direction of arrow 86, but moves upwardly slightly more slowly thanstep 56 descends. There is thus a certain very small time lag in therise of step 54 with the descent of step 56. It is however a finding ofthis invention that this time lag is not significant since the user doesnot particularly care what the unweighted step does as long as it movesupwardly at some time prior to the time that the user wishes to shifthis weight to this step. This being the case, it is not necessary toutilize mechanical phasing in order to satisfy the user's need forrealistic stair climbing experience. Note that there is a cushioning airbubble 87 at the top of each actuator to damp sharp hydraulic forceswhich may be applied to the end of the actuator rod by stamping on astep.

As the exercise stair is utilized, energy is imparted to the hydraulicfluid within the actuators. Under ordinary circumstances it is necessaryto accommodate the expansion that is built up by the energy imparted tothe fluid. However, as illustrated in FIG. 3, when heat is added to thehydraulic fluid, since the system is hydraulically open-ended, theexpansion of the fluid with heat results only in a rise in the positionof each of the steps as illustrated by dotted outlines 90. The positionof each of the steps will rise identically and is caused by an identicalextension in the positions of rods 78 as illustrated at 92.

Because of the open-ended hydraulic system, the amount of counterforceprovided by each step does not vary perceptibly during use even though aconsiderable amount of energy is added to the system. All that occurswith extended use is a simultaneous rise in the position of the steps.The resulting expansion of stroke is no problem to the user and it doesnot effect the exercise rate which is essentially a function of the rateof flow through orifice 84.

The advantages of the total hydraulic open-ended system are theresolution with which the climbing rate can be adjusted by valve 62, therepeatability of the exercise rate with the setting of valve 62, and theuniformity of the counterforce provided by the system. The rate at whichthe weight is shifted by the individual in the stair climbing exercisedoes not affect the counterforce to any perceptible degree and thus thesubject exercise device is speed independent. The exercise variable issolely the size of the restricted orifice as dictated by valve 62 whichsets the maximum rate at which the exercise can be performed, all otherparameters being equal, such as the size of the rods, viscosity of fluidover the operating temperature range, and the volume of the actuators.

Additionally, the force necessary to move a step downwardly is uniformover the exercise cycle and there is no starting friction to beovercome. Thus exercise may take place smoothly and at a uniform rateunlike most prior art devices.

With respect to safety, the most likely failure mode of the subjectexercise device is either fluid leakage around the seal, a rupture ofthe actuator, or a rupture of the interconnect lines 94 and 96 betweenactuators 60 and 58 and valve 62. Upon rupture of any of these lines oractuators, the result is the movement of the steps downwardly but at acontrolled rate. The rate is sufficiently slow to deposit the individualat the bottom of the tracks without harm.

TRACK/STEP DETAILS

Referring now to FIG. 5, a detailed cut away view of dual track 12 isillustrated in which like reference characters are utilized for likeelements as between FIG. 1 and FIG. 5. With respect to the individualtracks 40 and 42, the bottom portion of the track is made up of a plate100 which forms the back portion of the track. Channels 102 are mountedto plate 100 such that they are open to each other in pairs asillustrated, and carriages 50 and 52 are mounted in the tracks formed inthis manner. In one embodiment each carriage includes a double-plateconfiguration in which plates 101 and 103 are mounted in spaced-apartadjacency. The carriage has a rounded head portion 104 and roundedbottom corners 106. This double-plate frame is mounted to skids 108 and110 on either side thereof, with the skids mounted in a sliding fit tothe respective track. In a preferred embodiment the skids are made ofoil-impregnated wood to eliminate noise associated with systems whichuse rollers. As mentioned, the oil-impregnated wooden skid is as much as60% oil by weight.

Actuator 58 is mounted such that a top portion 112 extends through thedouble-plate structure in a slot (not shown), with the associated rod 78being attached at 114 to the top portion 104 of carriage 52. Because ofthe double-plate configuration of the carriage, as illustrated bycarriage 50, a major portion of the body of actuator 60 can extend tothe interior of the carriage as this carriage is moved downwardly. Thus,the actuator can be made relatively thin and relatively long. In oneembodiment the actuator has an inside diameter of 22 mm, with a rodhaving an outside diameter of 10 mm, the length of the actuator being 18inches and the length of the rod being 15 inches.

Base 112 of each actuator is mounted to a base plate 114 in a flexiblejoint generally indicated at 116, so as to accommodate off-axis movementas illustrated by dotted line 118. Each of the connecting lines betweenthe actuators, here illustrated at 120 and 122, has an intermediateflexible linkage 124 so as to accommodate the off-axis movement of theactuators. This flexible connection is illustrated in greater detail inFIG. 6.

Referring to FIG. 6, the base of actuator 60 is provided with an annulargroove 130 in which is located a C-ring 132 which limits the upwardmovement of a rigid washer 134 which bears down on a resilient gasket orwasher 136. C-ring 132 limits the downward movement of actuator 60,whereas an insert 140 prevents upward movement of actuator 60. In oneembodiment, insert 140 has an annular flange 142 and a cylindricalextension 144 which is friction fit to the exterior or outer dimensionof the base of actuator 60.

The resiliency of washer 136 permits off-axis movement of actuator 60 insuch a way that the actuator may cant relative to base plate 114. Anycanting of the actuator is accommodated by the resilient or flexibleconnection provided by linkage 124. This configuration permits limitedmovement of the actuators and reduces the amount of leakage at seal 82due to wear from side loading caused by manufacturing tolerances whichresult in lateral carriage motion within the tracks.

FOLDING FOR STORAGE

As mentioned, one of the features of the subject exercise stair is itseasy stowability due to its compact design. The containment of all ofthe hydraulics within the track permits the device to be folded suchthat the track lies against the support frame. As will be described,there are a number of methods for permitting this folding asdemonstrated by the devices of FIGS. 7, 9, 10, 11 and 12. Moreoverfoldable steps, telescoping arms and wheels shown in FIGS. 5 and 8 alsocontribute to the compact, portable design.

Referring to FIG. 5, step 56 is mounted to carriage 52 at hinge points144 and 146 in which the top portion of the step is hinged at 144. Anupstanding support 148 is hinged at 146, with step 56 being providedwith a downwardly projecting flange 150 having a slot 152 extendingalong the length thereof. The weight of an individual on a step urgespin 154 in the direction of arrow 156 until it reaches the end of slot152. Thus step 56 provides steady support for the weight of theindividual.

As also illustrated in FIG. 7, the steps may be collapsed for storageinto the plane of dual track 12 by moving step 56 up and then down. Thiscauses pin 154 to move in the direction of arrows 160 which causes step56 first to move upwardly and then downwardly as illustrated by arrow162 so that it moves to a position illustrated in phantom at 164, whichis an intermediate position. Thereafter, the step may be moved until itis flush with the top surface of track 12.

FIG. 7 also serves to show the collapsed configuration of the exercisestair in which frame 14 is folded flush with the track 12, with arms 22or 24 telescoped into the frame. The folding of the stair to itscollapsed position is a function of the double-hinged pivot 20. Theoperation of double-hinged pivot 20 will be described in connection withFIGS. 9 and 10.

Referring to FIG. 8, the collapsed exercise stair 10 may be easilypositioned under a bed 170 by virtue of wheels 38 and telescopinghandles 22 and 24 which effectively provide a wheelbarrow structure.

Referring now to FIG. 9, in one embodiment the assembly of the exercisestair from its collapsed position as illustrated in FIG. 7 to itsoperating position includes the swinging away of frame 14 from track 12as illustrated at dotted outline 180. In order to accomplish this, hingestrap 20 is rotated in the direction of arrow 182 with the pulling awayof the frame from the track. This movement is also illustrated by arrow184. Further movement as illustrated by arrow 186 causes frame 14 to berotated into place as illustrated at dotted outline 188, with the framebeing rotated about pivot 18 as illustrated by arrow 190. When inposition, end 192 of track 12 abuts a surface 194 of frame 14 so as toprovide for an extremely stable configuration.

As illustrated in FIG. 10, the stability of the FIG. 9 embodiment is inpart provided by the compression of member 192 against a plate 196carried on a face 194 of upstanding frame member 32. Here, member 192 isa cross-member having a flat face 196 which is wedged against the faceof plate 196 and is flush with and compressed thereto by virtue ofrotation of frame 12 in the direction of arrow 200. The downwardmovement of the lower edge 202 of member 192 is limited by a stop 204 sothat when face 198 is flush with plate 196, the downward travel ofmember 192 is limited. This compression and downward limiting stopprovides for an exceptionally stable assembly. The stability of thistype of tight fit utilizing a double-hinged strapped arch configurationis aided by the horizontal running cross piece 34 of the frame asillustrated in FIG. 1, and also by the horizontally running support 39for the lower edge of the track 12 of FIG. 1. Moreover, since the innerflat surfaces of the hinges are pressed to and overlap the sides of thetrack on either side, the track is prevented from moving laterally dueto the tight bolting of the hinges to the track and the structuralrigidity afforded by horizontal spacing member 36. Thus lateral movementof the exercise stair is prevented by the straps and the twohorizontally running members which contact the floor, whereas the strapsclamp the track to the frame, such that overall stability is provided bythe compression of the ends of the track with the upstanding framemembers. Note that the straps limit the separation between the bottomsof the track and frame.

Referring now to FIG. 11, the hinged attachment of the track to theframe may be implemented through the utilization of four straps asopposed to two. The use of a 4-bar linkage eliminates any unexpectedmotions of the frame relative to the track so that the device cannot beset up improperly. This eliminates the necessity for any skill on thepart of the user of the device since during folding, the frame goes fromperpendicular to the track to a position parallel to the track in acontrolled motion. Moreover the 4-bar linkage provides positivepositioning in the closed and open positions. In this embodiment a rigidstrap 205 is pivoted to track 12 at 206 and to frame 14 at 208. A secondrigid strap 209 is pivoted to frame 12 at 210 and to track 14 at 211such that when frame 14 is moved towards frame 12, it assumes a fixedset of angular orientations with respect to the frame as it moves fromits operating position to its folded position and visa-versa. This setof angular orientations is established by virtue of the utilization ofthe four straps and their multiple hinge points so that the frame cannotflop loosely at a number of different angles during set up and folding.What this accomplishes is that the orientation of the frame relative tothe track is established at a set of predetermined angles such that whenthe frame meets the track in the operating position, the frame is at theappropriate angular orientation α. At 14' midway through the swing ofthe frame from the track the frame assumes an angular orientation β withrespect to the track for the position of strap 205 shown at 205'. Notethat strap 206 prevents the frame from assuming position 212 at angularposition γ when strap 205 is at the 205' position. Thus the frame is notleft to flop loose between folded and open positions. Likewise at 14"when the frame is swung inwardly towards the track, it comes to restparallel to the track since its position is maintained by virtue of thefour straps.

In order to aid in the stability of the assembled device, a block 213 ispositioned to limit the upward movement of strap 205 such that whenstrap 205 rests against the bottom edge of block 213, frame 14 is in theproper position with respect to the track.

In an alternative embodiment, and referring now to FIG. 12, the frame214 may be divided into arms 215 and legs 216 as illustrated. Arms 215are pivoted to track 217 at pivot points 218 whereas legs 216 arepivoted to track 217 at pivot points one of which is shown at 219.Stabilizing bars 220 and 221 are provided respectively between the armsand the legs to provide lateral stability. The arms and legs aremaintained in the positions illustrated by straps 222 and 223, having acommon releasably engageable hinge pin 224 mounted through a slot 225 intrack 217. The other ends of straps 222 and 223 are pivotally mountedrespectively to legs 216 at 226 and to the arms at 227.

In operation, hinge pin 224 is held at the end of slot 225 asillustrated by the force exerted on legs 216. This in turn holds thearms in place. When it is desired to collapse and fold the arms and legsto the track, hinge pin 224 moves in the direction of arrow 228 as thearms and legs are moved in the direction of arrows 229.

In this embodiment the arms and legs are folded down to the plane of thetrack in a clam shell arrangement to provide an extremely compact andportable device. Setting up of the device merely entails movement of thearms and legs away from the track to the positions shown in FIG. 12.

What has been described are a number of alternative methods of providinga collapsible, compact, portable exercise stair in which props and armsmay be readily folded to the track for storage.

With respect to portability, as illustrated in FIG. 13, a back portion201 of the track plate 100 may be provided with a handle 203 such thatthe entire device may be carried as illustrated in this Figure.

PISTON CYLINDER EMBODIMENT

Referring now to FIG. 14, in an alternative embodiment steps 230 and 232may be hung from hydraulic cylinders 234 and 236 respectively, with eachof the steps being coupled to a respective cylinder by a rod 236 and 238respectively. Piston seals 240 are provided at the end of each of therods, with the end of the cylinders being mounted to a cross-member 242within a frame 244. A valve 246 is interposed in a line 248 whichcommunicates with the base of cylinder 234 at point 250, and with thebase of cylinder 236 at point 252. Rods 236 and 238 are joined at theirother ends to step frames 254 and 256 respectively.

In this embodiment the cylinders are hung from the top of the frame andthe steps are supported by rods which are in tension. It will beappreciated that rods in tension can be made smaller than rods incompression which translates into less weight and less cost. Also withthe hanging of the cylinders and the rods in tension, there is aconvenient self-alignment of the rods within their respective cylinders.

Moreover, in the FIG. 14 embodiment the hydraulic pressure is typicallymuch lower for the hydraulic ram embodiments of FIGS. 1-6. The reasonfor this is that the effective area of the piston can be larger in apiston cylinder than in a hydraulic ram. The lower operating pressureincreases the lifetime of the apparatus and is therefore of advantage.

Additionally, the effect of thermal expansion on stroke can be much lessin the piston cylinder embodiment as compared to the positivedisplacement cylinder. In one embodiment the thermal expansion isone-ninth that of the positive displacement cylinder embodiment.

As a further advantage to the hanging of the cylinders, is the abilityto place the adjustment valve in a more convenient position withoutcomplicated plumbing and thus higher cost.

Having above indicated a preferred embodiment of the present invention,it will occur to those skilled in the art that modifications andalternatives can be practiced within the spirit of the invention. It isaccordingly intended to define the scope of the invention only asindicated in the following claims.

What is claimed is:
 1. An exercise device comprising:a pair of inclinedside-by-side tracks; a pair of steps, each mounted for translation in adifferent one of said tracks and each unrestricted in the amount ofstroke during exercise, said steps being phased only hydraulically by anopen loop system such that increased fluid expansion during usuageresults only in the raising of the steps, thereby eliminating pressureincrease due to thermal expansion, said open loop system including saidsteps and a pair of hydraulic actuators for respective steps, eachactuator including a cylinder and a rod disposed therein, with one endof a rod supporting a respective step; means for coupling fluid from oneactuator to the other such that as one rod moves in one direction withinthe associated cylinder, the rod in the other cylinder moves in anopposite direction, said rods in unison being permitted to extendfurther up each cylinder during usage in accordance with the expansionof the fluid volume in the system due to the energy introduced into thesystem during usage such that the thermally induced pressure within thesystem stays substantially contant; and, fluid metering means interposedin said coupling means and including a variable restricted orifice, thesize of said orifice determining the fluid flow rate, the steppingfrequency, and thus the exercise rate, whereby excercise rate may beeasily adjusted.
 2. The exercise device of claim 1 wherein saidactuators are hydraulic rams.
 3. The exercise device of claim 1 whereinsaid hydraulic cylinders have rods sealed to a respective cylinder onlyat one end of the cylinder.
 4. The exercise device of claim 3 whereinsaid fluid coupling means includes a fitting at the end of a cylinderopposite that at which a rod is sealed, a conduit from one fitting tosaid fluid metering means and a conduit from said fluid metering meansto the other of said fittings.
 5. The exercise device of claim 4 whereinsaid conduits are flexible.
 6. The exercise device of claim 5 whereineach of said tracks includes a cross member adjacent the base thereofand further including flexible means for mounting the end of thecylinder having said fitting to said cross member.
 7. The exercisedevice of claim 1 wherein each of said rods includes a piston seal atone end of said rod.
 8. The exercise device of claim 7 and furtherincluding means for mounting said cylinders at the top of respectivetracks such that said rods depend towards the base of said tracks andmeans for suspending said steps from the ends of respective rods.
 9. Theexercise device of claim 1 and further including means includingoilimpregnated skids for supporting said steps in said tracks.
 10. Theexercise device of claim 9 wherein said skids are made of wood.